JP5168898B2 - Rolling shaft - Google Patents

Description

  The present invention relates to a rolling shaft that rolls relative to a rolling element that is a counterpart member.

  The pinion shaft of the conventional planetary gear device is composed of JIS steel grade SK5 or the like, and the portion (rolling surface) where the needle roller rolls is hardened to give the necessary hardness as the pinion shaft. It was. Further, when the peeling life due to poor lubrication or the like becomes a problem, the pinion shaft is made of JIS steel type SUJ2 or the like, and is subjected to carbonitriding or the like to ensure the life.

In recent years, there has been an increasing demand for lower fuel consumption in automobiles, and transmissions are becoming smaller and more efficient. Therefore, since the rotational speed of the planetary gear device is increasing, the load applied to the pinion shaft increases, the temperature rises, and the amount of lubricating oil tends to decrease, leading to a reduction in the life of the pinion shaft. .
Furthermore, since the temperature increases as the load increases, plastic deformation is likely to occur in the pinion shaft. As a result of this deformation, slippage between the needle roller and the pinion shaft increases to cause wear and peeling of the raceway surface, and contact between the needle roller and the pinion shaft becomes an edge load, leading to early peeling. There is a risk of problems.

  The plastic deformation of the pinion shaft is a phenomenon in which bending occurs in the direction of relaxing the load applied to the pinion shaft. This plastic bending tends to increase as the amount of retained austenite inherent in the steel increases. For this reason, in order to suppress plastic bending, it is most important to reduce the amount of retained austenite as much as possible. However, if the amount of retained austenite on the rolling surface of the pinion shaft is small, the rolling fatigue life is lowered, and the required durability may not be obtained.

  Rolling bearings used in planetary gear units are sometimes used under conditions of high temperature, high speed, and light load, and the pinion shaft rolling surface is filled with hard foreign matter mixed in the lubricating oil. Surface-origin-type delamination starting from an indentation due to or smearing that tends to occur under light load occurs early, and the bearing life may be significantly reduced. Therefore, if the pinion shaft is made of steel such as SK5 or SUJ2, a sufficient bearing life may not be obtained under conditions of high temperature, high speed, and light load.

In addition, rolling bearings used in planetary gear devices are sometimes used under conditions of high temperature, high load, high vibration, and insufficient lubrication, and are not easily corroded at the maximum shear stress position under the rolling surface, and are whitened with an optical microscope. Visible white texture may occur and the rolling life may be significantly reduced. The structural change that causes the damage is caused by hydrogen in the lubricating oil being decomposed by local metal contact and entering the steel. Therefore, if the pinion shaft is made of steel such as SK5 or SUJ2, a sufficient bearing life may not be obtained under the conditions of high temperature, high load, high vibration, and insufficient lubrication.
Japanese Patent Laid-Open No. 2002-4003 JP 2005-291342 A

Patent Document 1 discloses a method for suppressing plastic bending of a pinion shaft by performing tempering after carbonitriding and subsequently performing induction hardening so that the amount of retained austenite in the core is 0% by volume. Yes. And the rolling fatigue life is improved by hardening a surface layer part by induction hardening.
However, if the pinion shaft is made of steel such as SUJ2, S55C, SAC5160, and SCr420 exemplified in the embodiment of Patent Document 1, rolling that can withstand high-speed rotation, contamination of the lubricant, and insufficient supply When it is difficult to ensure the fatigue life, or depending on the use conditions, smearing or white peeling may occur, and problems such as early peeling may occur. In addition, induction hardening has room for improvement in terms of management and cost.

Patent Document 2 discloses a method for suppressing plastic bending by setting the average retained austenite amount to 8% by volume or less. However, in order to suppress plastic bending, it is not sufficient to specify the average retained austenite amount. For example, even if the average amount of retained austenite is the same, if the difference between the amount of retained austenite in the surface layer and the amount of retained austenite in the core is small, the amount of plastic deformation in the surface layer (decomposition of retained austenite) and the plastic deformation in the core The amount (decomposition of retained austenite) is close to the amount, and the force to return the pinion shaft to the original shape when the load or centrifugal force is unloaded becomes small, so the amount of plastic bending of the pinion shaft may increase.
Therefore, the present invention solves the problems of the prior art as described above, and is plastically deformed even when used under high temperature, poor lubrication, contamination with foreign matter, or in an environment where smearing or white texture is likely to occur. It is an object of the present invention to provide a rolling shaft that is less likely to cause the occurrence of wear.

In order to solve the above problems, the present invention has the following configuration. That is, the rolling shaft according to the first aspect of the present invention is characterized in that the following seven conditions are satisfied in the rolling shaft that rolls relative to the rolling element as the counterpart member.
Condition 1: carbon is 0.3 mass% or more and 0.5 mass% or less, chromium is 2 mass% or more and 5 mass% or less, molybdenum is 0.1 mass% or more and 1.5 mass% or less, and manganese is 0.1 mass%. % To 1.5% by mass, silicon is contained in an amount of 0.1% to 1.5% by mass , and the balance is made of iron and alloy steel that is an inevitable impurity .

Condition 2: A surface layer portion formed by carburizing or carbonitriding, quenching and tempering and hardening is formed on the surface sliding with the rolling element, and the surface hardness Hv is 650 or more and 900 or less. Has been.
Condition 3: The amount of retained austenite in the surface layer portion is 5% by volume or more and 45% by volume or less. Condition 4: The amount of retained austenite in the core part inside the surface layer part is 5% by volume or less.

Condition 5: The amount of retained austenite in the surface layer portion is 6 to 12.5 times the amount of retained austenite in the core portion.
Condition 6: The sum of the carbon concentration and the nitrogen concentration in the surface layer part is 0.8% by mass or more and 2% by mass or less.
Condition 7: The rate of dimensional change due to holding at 170 ° C. for 100 hours is 1.5 × 10 ⁻⁴ or less.

  The rolling shaft of the present invention is excellent in durability because it hardly undergoes plastic deformation even when used under high temperatures, poor lubrication, contamination with foreign matter, or in an environment where smearing or white texture is likely to occur.

An embodiment of a rolling shaft according to the present invention will be described in detail with reference to the drawings.
The planetary gear device shown in FIG. 1 is suitably used for a planetary gear mechanism such as an automatic transmission for automobiles, and includes a sun gear 1 through which a shaft (not shown) is inserted, and a ring gear 2 arranged concentrically with the sun gear 1. And one or more (three in FIG. 1) pinion gears 3 that mesh with the sun gear 1 and the ring gear 2 and revolve around the sun gear 1, and are arranged concentrically with the sun gear 1 and the ring gear 2 to rotatably support the pinion gear 3. And a carrier 4.

  A pinion shaft 5 (corresponding to the rolling shaft of the present invention) fixed to the carrier 4 by caulking or the like is inserted into the center hole of the pinion gear 3, and the outer peripheral surface of the pinion shaft 5 and the inside of the pinion gear 3 are inserted. A plurality of needle rollers (not shown) (corresponding to rolling elements that are mating members of the rolling shaft) are arranged so as to be able to roll between the peripheral surfaces, whereby the pinion gear 3 has the pinion shaft 5 as an axis. The pinion shaft 5 corresponds to the inner ring of the rolling bearing.

  This pinion shaft 5 has a carbon content of 0.3% to 0.5%, chromium content of 2% to 5%, molybdenum content of 0.1% to 1.5%, and manganese content of 0%. The alloy steel contains 0.1% by mass or more and 1.5% by mass or less and silicon by 0.1% by mass or more and 1.5% by mass or less. Since the pinion shaft 5 is subjected to carburizing or carbonitriding, quenching and tempering, a hardened surface layer portion is formed on the outer peripheral surface, and the surface hardness Hv is 650 to 900. Has been. Therefore, the hardened surface layer portion is also formed on the portion of the outer peripheral surface that slides with the needle rollers (hereinafter also referred to as a rolling surface).

  And the amount of retained austenite of the surface layer part is 5 volume% or more and 45 volume% or less, the amount of retained austenite of the core part inside the surface layer part is 5 volume% or less, and the amount of retained austenite of the surface layer part is the core part. The amount of retained austenite is 6 times or more. Further, the sum of the carbon concentration and the nitrogen concentration in the surface layer portion is 0.8 mass% or more and 2 mass% or less.

The planetary gear device having such a configuration is less likely to be plastically deformed in the pinion shaft 5 even when used in an environment where high temperatures, poor lubrication, foreign matter contamination, or smearing or white texture is likely to occur. Excellent durability. Further, such a pinion shaft 5 is not easily deformed even when held at 170 ° C. for 100 hours, and its dimensional change rate is 1.5 × 10 ⁻⁴ or less. With such a dimensional change rate, a dimensional change at a high temperature is suppressed. When the dimensional change rate is larger than 1.5 × 10 ^{−4, in} the case of the pinion shaft of the planetary gear device, the contact surface is locally generated by edge load due to plastic bending or reduction of radial gap due to expansion or deformation of the diameter. There is a risk that the pressure will increase and the rolling life will decrease.

  The decrease in the rolling life of the planetary gear device under the mixing of foreign matter is caused by stress concentration at the rising edge of the indentation formed by the biting of the foreign matter. When the surface hardness Hv of the pinion shaft is 650 or more and 900 or less, the rolling surface of the needle roller is sufficiently hard and an indentation is not easily formed, so that it has a long life even when used in the presence of foreign matter. If the surface hardness Hv is less than 650, indentation may be formed because the hardness is insufficient, and if it exceeds 900, it is necessary to increase the quenching temperature. As a result, the toughness may be reduced.

  Further, when the amount of retained austenite in the surface layer portion is 5% by volume or more and 45% by volume or less, stress concentration as described above hardly occurs. If it is less than 5% by volume, the effect of reducing the stress concentration that relieves surface fatigue is poor, and the fatigue life is reduced. On the other hand, if it exceeds 45% by volume, the surface hardness becomes insufficient and the wear resistance and surface fatigue resistance may be impaired. In order that such inconvenience is less likely to occur and an excellent fatigue life can be stably obtained, the amount of retained austenite in the surface layer portion is more preferably 10% by volume or more and 40% by volume or less.

  Further, the retained austenite is decomposed and changed into a mixture of ferrite and cementite or martensite when stress such as a load or heat is applied, so that plastic deformation occurs in the pinion shaft. Therefore, if the amount of retained austenite in the surface layer is 6 times or more than the amount of retained austenite in the core, the difference between the amounts of retained austenite is large, and the force to restore the pinion shaft to its original shape when the load or centrifugal force is unloaded. Since it becomes large, it is possible to suppress the plastic bending of the pinion shaft.

  Further, the presence of residual austenite in the surface layer portion improves the rolling fatigue life, and the amount of residual austenite in the core portion is reduced as much as possible to suppress the plastic bending of the pinion shaft. The amount of retained austenite in the core portion needs to be 5% by volume or less, and more preferably 0% by volume. In order to reduce the amount of retained austenite in the core, it is preferable to set the treatment temperature to 150 ° C. or more and 300 ° C. or less in the tempering as the final step of the heat treatment. If the tempering temperature is too high, the retained austenite in the surface layer portion is reduced, which may cause a reduction in rolling life. In order to make the amount of retained austenite in the surface layer portion 5% by volume or more, the tempering temperature is more preferably 270 ° C. or less.

  Furthermore, when the sum of the carbon concentration and the nitrogen concentration in the surface layer portion is 0.8% by mass or more and 2% by mass or less, the wear resistance, rolling fatigue resistance, and heat resistance are excellent. If it is less than 0.8% by mass, the precipitation of carbonitride effective for improving the wear resistance becomes insufficient, and the wear resistance may be lowered. Moreover, the amount of retained austenite in the surface layer portion is less than 5% by volume, which may cause a reduction in rolling life. On the other hand, if it exceeds 2% by mass, it is advantageous for improving the wear resistance, but the pro-eutectoid carbide is generated in a net shape and the rolling life is reduced, the productivity of heat treatment is reduced, Or there exists a possibility that the grindability after heat processing may fall. Further, the Ms point is lowered too much and the amount of retained austenite exceeds 45% by volume, and as a result, the surface hardness Hv may be less than 650. In order to further improve performance such as wear resistance, rolling fatigue resistance, and heat resistance, the sum of the carbon concentration and the nitrogen concentration in the surface layer portion is preferably 1% by mass or more and 1.8% by mass or less.

Here, the critical significance of the content of the alloy component contained in the alloy steel will be described.
[Carbon content]
Carbon (C) is solid-solved in the base to improve the hardness after quenching and tempering to improve the strength and combine with carbide-forming elements such as iron, chromium, molybdenum, vanadium to form carbides and resist It is an element that has the effect of increasing wear. If the time of carbonitriding performed to obtain the hardness required for rolling fatigue resistance is increased, the cost is increased, so that the carbon content is 0.3% by mass or more in order to shorten the processing time. There is a need. However, if it exceeds 0.5% by mass, coarse eutectic carbides are likely to be produced during steelmaking, and the rolling life and strength may decrease. In addition, forgeability, cold workability, and machinability may decrease, resulting in an increase in processing cost.

[Chromium content]
Chromium (Cr) is an element having a function of improving the hardenability, temper softening resistance, corrosion resistance, and rolling life by dissolving in a matrix. It also has the effect of stabilizing the base structure by making it difficult for movement of interstitial solid solution elements such as carbon and nitrogen to greatly reduce the lifespan during hydrogen intrusion. Furthermore, since the carbide finely distributed in the alloy steel is composed of carbides such as (Fe, Cr) ₃ C, (Fe, Cr) ₇ C ₃ , (Fe, Cr) ₂₃ C _{6 and the} like having higher hardness, It also has the effect of increasing wear resistance. Further, the retained austenite is not easily decomposed by heat, and as a result, plastic deformation is difficult.

  If the chromium content in the alloy steel is less than 2% by mass, the above-mentioned effects may not be obtained sufficiently. If it exceeds 5% by mass, cold workability, machinability and carbonitriding will There is a risk of lowering the cost. Furthermore, coarse eutectic carbides are likely to be generated during steelmaking, and the rolling life and strength may be reduced.

[Molybdenum content]
Molybdenum (Mo) is an element having the effect of increasing the hardenability, temper softening resistance, corrosion resistance, and rolling life by solid solution in the base like chromium. In addition, like chromium, interstitial solid solution elements such as carbon and nitrogen are made substantially difficult to move to stabilize the base structure, and have the effect of greatly suppressing the decrease in life at the time of hydrogen intrusion. Furthermore, since the carbide finely distributed in the alloy steel is made of a carbide of molybdenum having a higher hardness, it also has an effect of improving wear resistance.

  If the molybdenum content in the alloy steel is less than 0.1% by mass, the above-mentioned effects may not be sufficiently obtained. If the content exceeds 1.5% by mass, cold workability and machinability are obtained. There is a risk of lowering the cost. Furthermore, coarse eutectic carbides are likely to be generated during steelmaking, and the rolling life and strength may be reduced.

[About manganese content]
Manganese (Mn) is an element that acts as a deoxidizer during steelmaking, and it is necessary to add 0.1 mass or more. Moreover, it has the effect | action which solid-dissolves to a base | substrate similarly to chromium, and lowers Ms point, ensures a large amount of retained austenite, or improves hardenability. However, if added in a large amount, not only the cold workability and machinability are lowered, but also the martensitic transformation start temperature is lowered, and a large amount of retained austenite remains after carbonitriding and sufficient hardness cannot be obtained. There is a case.

[About silicon content]
Silicon (Si) is an element that acts as a deoxidizing agent during steelmaking, like manganese, and it is necessary to add 0.1 mass or more. Moreover, it is an element effective in improving the bearing life by improving the hardenability as well as chromium and manganese, and promoting the martensitic transformation of the base and the stabilization of retained austenite. Furthermore, it has the effect | action which raises temper softening resistance. However, if it is added in a large amount, forgeability, cold workability, machinability, and carburizing property may deteriorate.

  In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the present embodiment, the pinion shaft of the planetary gear device has been described as an example. However, the rolling shaft of the present invention can be applied as a member corresponding to an inner ring of various other types of rolling bearings.

〔Example〕
The present invention will be described more specifically with reference to the following examples. A pinion shaft having substantially the same configuration as the pinion shaft 5 in the above embodiment is manufactured by the following method, and a rolling fatigue life test, a white peeling life test, a smearing test, a dimensional stability test, and a plastic bending are performed. Measurements were made.

  Here, the manufacturing method of the pinion shaft used for various tests is demonstrated. As the material for the pinion shaft, 12 kinds of alloy steels having the compositions shown in Table 1 were used. The wire made of the alloy steel was subjected to turning, heat treatment, outer diameter rough grinding, outer diameter finishing grinding, and superfinishing grinding to obtain a pinion shaft having a diameter of 14.17 mm and a length of 70 mm. Properties of the obtained pinion shaft, that is, the hardness Hv and the retained austenite amount of the surface layer portion, the hardness Hv and the retained austenite amount of the core portion, the ratio of the retained austenite amount of the surface layer portion and the retained austenite amount of the core portion, and the surface layer Tables 2 and 3 show the sum of the carbon concentration and the nitrogen concentration in parts. Moreover, the process temperature of the last tempering mentioned later among heat processing is combined with Table 2, 3, and is shown.

The contents and conditions of the heat treatment are as follows. A cylindrical member obtained by turning an alloy steel wire is subjected to carbonitriding at 820 to 980 ° C. for 3 to 5 hours, and then tempered at 150 to 200 ° C. for 1.5 hours. did. This carbonitriding process was performed in an atmosphere containing RX gas, enriched gas, and ammonia gas. Next, quenching was performed under the conditions of 860 to 950 ° C. and 0.5 hours, and finally tempering was performed under the conditions of 150 to 300 ° C. and 1.5 hours. In addition, about the comparative example 10, the carbonitriding process is not performed, and the content of the heat processing is only a submerged quenching and the last tempering. In order to stabilize the structure, it is preferable to cool to a temperature lower than the A ₁ transformation point between carbonitriding and quenching.

[Rolling fatigue life test]
The pinion shaft was attached to a planetary needle testing machine manufactured by NSK Ltd. That is, the pinion shaft is inserted into the center hole of the pinion gear, and a plurality of needle rollers are interposed between the outer peripheral surface of the pinion shaft and the inner peripheral surface of the pinion gear so as to roll freely. As a result, the pinion gear is rotatable about the pinion shaft. This needle roller is made of high carbon chrome steel (SUJ2), and its dimensions are 2.5 mm in diameter and 24.8 mm in length. Further, the needle rollers are held by a cage made of JIS steel type SCM415 to form a cage and roller. The cage is carbonitrided.

  Then, a rotation test was performed under the following conditions, and it was determined that at least one of the pinion shaft, the pinion gear, and the needle roller had reached the end of its life, and the rotation time until that time was defined as the rolling fatigue life. The results are shown in Tables 4 and 5. In addition, the rolling fatigue life of Tables 4 and 5 is shown as a relative value when the rolling fatigue life of Comparative Example 10 is 1. In addition, a preliminary test is performed to determine which member of the pinion shaft, pinion gear, and needle roller is most likely to be damaged, and a rotation test is performed after confirming that the pinion shaft is most easily damaged.

・ Basic dynamic load rating C: 15500N
・ Basic static load rating C ₀ : 16700N
・ Radial load: 5000N
-Spinning speed of pinion gear: 10000 min ^-1
- calculated life L _10: 72.4 hours, lubricants Type: supply of automatic transmission fluid, lubricating oil: 30 ml / min
Lubricating oil temperature: 120 ° C

  As can be seen from Table 4.5, Examples 1 to 12 were superior in rolling fatigue life compared to Comparative Examples 1 to 10. Comparative Example 1 had a short rolling fatigue life because the amount of retained austenite in the surface layer portion was small and the effect of reducing stress concentration to relieve surface fatigue was insufficient. In Comparative Example 2, since the amount of retained austenite in the surface layer portion is too large and the surface hardness is less than Hv650, indentations may be formed on the rolling surface.

  In Comparative Example 3, since the ratio of the amount of retained austenite in the surface layer portion and the amount of retained austenite in the core portion did not satisfy the above-described conditions, the plastic bending of the pinion shaft was increased and the rolling fatigue life was shortened. In Comparative Example 4, since the amount of retained austenite in the core part was too large, the plastic bending became large and the rolling fatigue life was short. In Comparative Example 5, since the sum of the carbon concentration and the nitrogen concentration in the surface layer portion was low, the wear resistance, rolling fatigue resistance, and heat resistance were insufficient, and the rolling fatigue life was shortened.

  In Comparative Example 6, the alloy steel had a high carbon content and the core portion had a large amount of retained austenite, so that the rolling fatigue life was shortened due to plastic bending. In Comparative Example 7, since the chromium content of the alloy steel was small, the wear resistance due to chromium carbide was insufficient, and the rolling fatigue life was shortened. In Comparative Example 8, since the manganese content of the alloy steel was small, the Ms point decreased and the amount of retained austenite in the surface layer portion decreased. For this reason, the stress concentration reducing effect to relieve surface fatigue is insufficient, and the rolling fatigue life is shortened.

  In Comparative Example 9, since the molybdenum content of the alloy steel was small, the wear resistance due to molybdenum carbide was insufficient, and the rolling fatigue life was shortened. Comparative Example 10 is a pinion shaft manufactured by subjecting SUJ2 to quench hardening. However, the bending fatigue resistance of the material is insufficient, and the amount of retained austenite in the surface layer and core portion causes plastic bending and dimensional changes. Due to the large (expansion), the rolling fatigue life was short.

[About white peel life test]
When a rotation test is performed in the same manner as the rolling fatigue life test described above except that the radial load and other conditions are different as described below, and when white peeling occurs on at least one of the pinion shaft, pinion gear, and needle roller The rotation time up to that time was defined as the white peeling life. The results are shown in Tables 4 and 5.
・ Radial load: 8000N
・ Calculated life L ₁₀ : 15.1 hours

In addition, the white peeling lifetime of Tables 4 and 5 is shown as a relative value when the white peeling lifetime of Comparative Example 10 is 1. In addition, a preliminary test is performed to determine which member of the pinion shaft, pinion gear, and needle roller is most likely to cause white separation, and a rotation test is performed after confirming that the pinion shaft is most likely to occur.
As can be seen from Table 4.5, Examples 1 to 12 were superior in white peel life as compared to Comparative Example 10.

[About smearing test]
The pinion shaft was attached to a planetary needle testing machine manufactured by NSK Ltd. That is, the pinion shaft is inserted into the center hole of the pinion gear, and a plurality of needle rollers are interposed between the outer peripheral surface of the pinion shaft and the inner peripheral surface of the pinion gear so as to roll freely. As a result, the pinion gear is rotatable about the pinion shaft. This needle roller is made of high carbon chrome steel (SUJ2), and its dimensions are 2.62 mm in diameter and 24.8 mm in length. Moreover, the retainer which hold | maintains a needle roller is not used, but is a full roller type.

And it rotated for 100 hours on the following conditions, and it was confirmed whether smearing had generate | occur | produced in the pinion shaft. The results are shown in Tables 4 and 5. As a result, smearing did not occur in Examples 1-12.
・ Basic dynamic load rating C: 24400N
・ Basic static load rating C ₀ : 29600N
・ Radial load: 500N
-Spinning speed of pinion gear: 10000 min ^-1
- calculated life L _10: 70 million hours · P / C (P: dynamic equivalent load, C: basic dynamic load rating): 0.02
・ Lubricant type: Automatic transmission fluid ・ Lubricant supply amount: 10 ml / min
Lubricating oil temperature: 120 ° C

[Dimensional stability test]
The dimensions were measured after holding the pinion shaft at 170 ° C. for 100 hours, and the dimensional change rate was calculated from the dimensions before and after holding. The results are shown in Tables 4 and 5. From this result, it can be seen that Examples 1 to 12 have better dimensional stability than Comparative Example 10.

[About plastic bending measurement]
Using a surfcom shape measuring machine, the amount of bending of the pinion shaft after the above-described rolling fatigue life test was measured. The measured value is a distance in a load application direction (a direction perpendicular to the axial direction of the pinion shaft) between a line connecting both ends of the pinion shaft and a portion farthest from the line. The results are shown in Tables 4 and 5.

The smaller the amount of retained austenite in the core part and the larger the ratio of the retained austenite amount in the surface layer part and the retained austenite amount in the core part, the smaller the plastic bending tends to be. Because they are different, a simple comparison is not possible.
Therefore, focusing on Example 1 and Comparative Example 3, Example 1 has a larger amount of retained austenite in the surface layer portion (the amount of retained austenite in the core portion is the same). Moreover, although the rotation time in a rolling fatigue life test is 2 times or more, Example 1 has a larger ratio of the above-mentioned residual austenite amount. From these facts, the plastic bending seems to be smaller in Example 1.

When attention is paid to Comparative Example 3 and Comparative Example 4, the rotation time in the rolling fatigue life test is almost the same, and the amount of retained austenite in the surface layer portion and the core portion is larger in Comparative Example 4. Further, the ratio of the amount of retained austenite is larger in Comparative Example 4. From these facts, it seems that the plastic bending is almost the same.
As in Comparative Examples 6 and 10, it can be seen that when the ratio of the retained austenite amount is less than 6 and the retained austenite amount in the core is large, the plastic bending is remarkably increased.

It is a disassembled perspective view of the planetary gear apparatus provided with the pinion shaft which is one Embodiment of the rolling shaft of this invention.

Explanation of symbols

1 Sun Gear 2 Ring Gear 3 Pinion Gear 4 Carrier 5 Pinion Shaft

Claims (1)

A rolling shaft that rolls relatively with respect to a rolling element that is a counterpart member, wherein the following seven conditions are satisfied :
Condition 1: carbon is 0.3 mass% or more and 0.5 mass% or less, chromium is 2 mass% or more and 5 mass% or less, molybdenum is 0.1 mass% or more and 1.5 mass% or less, and manganese is 0.1 mass%. % To 1.5% by mass, silicon is contained in an amount of 0.1% to 1.5% by mass , and the balance is made of iron and alloy steel that is an inevitable impurity .
Condition 2: A surface layer portion formed by carburizing or carbonitriding, quenching and tempering and hardening is formed on the surface sliding with the rolling element, and the surface hardness Hv is 650 or more and 900 or less. Has been.
Condition 3: The amount of retained austenite in the surface layer portion is 5% by volume or more and 45% by volume or less. Condition 4: The amount of retained austenite in the core part inside the surface layer part is 5% by volume or less.
Condition 5: The amount of retained austenite in the surface layer portion is 6 to 12.5 times the amount of retained austenite in the core portion.
Condition 6: The sum of the carbon concentration and the nitrogen concentration in the surface layer part is 0.8% by mass or more and 2% by mass or less.
Condition 7: The rate of dimensional change due to holding at 170 ° C. for 100 hours is 1.5 × 10 ⁻⁴ or less.

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